The charges against Mr. Navalny, that he embezzled the equivalent of $500,000 from a state timber company while acting as advisor to a regional governor, sound plausible enough. And he was convicted, in a court of law. "Navalny. . . committed a grave crime," said Judge Sergei Blinov as he passed a five year prison sentence on Navalny Thursday.

The key reason that many long-term observers of Russia have arrived at this conclusion is that Navalny, who is one of Russia's best-known opposition figures due to his highly-effective anticorruption blogging, is far from the only anti-Kremlin politician to have been targeted with elaborate criminal charges.

One of the first was oil tycoon Mikhail Khodorkovsky, who may have made his fortune through dubious methods in the 1990s along with numerous other "oligarchs," but was only arrested and charged with tax evasion 10 years ago after he refused to stop supporting opposition politicians and funding critical civil society groups. Legal experts have disputed the state's case against Mr. Khodorkovsky, and a court clerk told journalists that his second trial in 2011 was thoroughly stage-managed by the Kremlin, but he remains defiant and – some say therefore – is kept in prison. Many recent signals suggest that the Kremlin's powerful Investigative Committee is preparing a third trial against Khodorkovsky to keep the renegade oligarch in his Siberian penal colony after his second term expires next year.

Two parliamentarians who supported the protest movement, Gennady Gudkov and Ilya Ponomaryov, have faced endless legal woes. Among other things, Mr. Gudkov was expelled from the Duma last year, while Mr. Ponomaryov has been named by the Investigative Committee in a still-developing corruption scandal that may expand to include government figures who failed to crack down on the protest movement.

Early this month Yevgeny Urlashov, the popular mayor of Yaroslavl, one of Russia's largest cities, was arrested and charged with soliciting a bribe of about $500,000. Mr. Urlashov, who had defeated a candidate of the pro-Kremlin United Russia party, taking almost 70 percent of the vote, was planning to head an opposition slate for September regional elections.

No one assumes that liberals or leftists in power are necessarily any less corrupt than pro-Kremlin politicians, and Urlashov's case might not be remarkable if he were the only one. But according to a study by political scientist Mikhail Tulsky, about 50 independent mayors, or over 90 percent of all non-United Russia mayors elected to lead Russian municipalities, have been arrested or removed from office on a variety of criminal pretexts over the past three years.

Kremlin supporters have two responses to all this. First, they argue, criminals always shout "political persecution" when they get nabbed. Second, they say, critics like Mr. McFaul and Mr. Gorbachev are motivated by political animus against Putin and Russia. It's in their interests to transform people like Navalny into martyrs.

Opinion polls show that Putin remains extremely popular, with public approval ratings that routinely top 60 percent. Opposition figures, including Navalny, have little name recognition among the Russian population – at least outside of Moscow and other large cities – and miniscule support even among those who know of them.

That question still can't be definitively answered, though grounds for skepticism are growing by the day.

But before anyone concludes that such skepticism about the state of Russia's institutions is the invention of ill-intentioned Western journalists and diplomats, joined by Russia's beleaguered liberals, consider this May public opinion survey by the independent Levada Center in Moscow, which clearly shows that it's far-and-away the majority view among ordinary Russians.

When asked "Do you think that the trial of Alexei Navalny is the result of his political activities and his opposition views?" 59 percent of Russians answered "yes" while just 19 percent said "no."